This project, together with related investigations on the genetics of vocal behavior, aims eventually to contribute to understanding the mechanisms linking genes, brain circuits, and behavior. The research is currently focusing on identifying the cerebral mechanisms accounting for the structure and production of the isolation call. This vocalization, which is the most conspicuous behavioral manifestation of separation-induced distress, is produced in the laboratory by squirrel monkeys of all ages, and is, therefore, a useful behavioral probe for studying the physiology of vocal communication in that species. Current experiments in this collaborative project suggest that portions of the medial frontal limbic cortex, including in particular the posterior gyrus rectus, are necessary for spontaneous production of the isolation call. Other experiments involving structures more closely related to vocal effector mechanisms demonstrated that bilateral ablation of the lateral central gray matter and adjoining tegmental structures at the caudal level of the inferior colliculus eliminated a broad spectrum of vocalizations, including the isolation call. The region in question is believed to encompass a pathway leading to the motor neurons of the larynx (Nucleus ambiguus). Related studies employing behavioral pharmacology methods have extended previous findings in this project by showing that the morphine-induced elimination of isolation is not due to a general sedative effect.